Strapping machines apply a steel or polymeric strap in a sealed tensioned loop about a package to securely bind the package for shipping, storage and merchandising. Strapping machines generally comprise a strap feeding mechanism that forms the strap in a loop which surrounds a package to be bound. A strap take up mechanism then takes up any excess strap and may also apply a tension to the strap so that the strapping machine may perform additional functions on the strap, such as gripping and sealing the strap. It has been suggested to take up strap in a strapping machine by frictionally engaging a portion of the strap disposed between a pair of counter-rotating rollers rotated at a fixed rotation rate by a motor driven shaft journaled to a frame. Fixed rotation rate strap take up mechanisms have the disadvantage that they subject the strap to considerable mechanical stress and damage that may result in breakage of the strap during application of the strap about the package or during later handling of the bound package. Mechanical stress is not limited to the strap but also to the strap take up mechanism which may be subject to considerable frictional forces during strap take up. Mechanical stress to the strap and the strap take up mechanism is compounded by increased tension applied by the strap during strap take up. There exists therefore a demonstrated need for an advancement in the art of strap take up in a strapping machine.
It is an object of the present invention to provide a novel method and apparatus for a strap take up usable in a strapping machine.
It is also an object of the invention to provide a novel method and apparatus for a two speed strap take up usable in a strapping machine.
It is also an object of the invention to provide a novel method and apparatus for a two speed strap take up usable in a strapping machine that reduces a rate of strap take up in response to an increased strap resistance during strap take up.
It is also an object of the invention to provide a novel method and apparatus for a two speed strap take up usable in a strapping machine that is economical to practice and manufacture.
It is another object of the invention to provide a novel method and apparatus for a strap take up usable in a strapping machine that minimizes damage to a strap during take up.
It is a further object of the invention to provide a novel method and apparatus for a two speed strap take up usable in a strapping machine that prevents strap milling.
It is yet a further object of the invention to provide a novel method and apparatus for a two speed strap take up useable in a strapping machine that prevents strap pre-seal.
Accordingly, the present invention is directed toward a novel method and apparatus for a two speed strap take up usable in a strapping machine. The two speed strap take up apparatus generally comprises a high speed roller assembly driven by a high speed drive shaft, a low speed roller assembly driven by a low speed drive shaft, a shaft rotation reduction assembly interconnecting the high speed drive shaft and the low speed drive shaft, and a roller clutch assembly interconnecting the shaft rotation reduction assembly and the low speed drive shaft. An input clutch assembly may interconnect the high speed drive shaft and an input drive means. In operation, a strap is disposed between and frictionally engaged by a high speed roller of the high speed roller assembly and a low speed roller of the low speed roller assembly. The low speed roller is then driven in rotation, in an over-driven condition, by the high speed roller. When a first tension is applied to the strap, the high speed roller slips relative to the high speed drive shaft, this slippage causes rotational speed reduction of both rollers until the roller clutch interconnecting the shaft rotation reduction assembly to the low speed drive shaft engages and rotates the low speed drive shaft at reduced rotation rate relative to the rotation rate of the high speed drive shaft. In one embodiment, the ratio of high to low speed is on the order of 2:1. The high speed roller is then driven in rotation by the low speed roller as the high speed roller slips relative to the high speed drive shaft. When a second tension, greater than the first tension, is applied to the strap, the low speed roller slips relative to the low speed drive shaft at which time both rollers will stop rotating and the strapping machine may perform additional functions on the strap.
These and other objects, features and advantages of the present invention will become apparent upon consideration of the following Detailed Description of the Invention with the accompanying drawings.